How are percentiles used?

For the design of the vertical space available above a seat surface, for example for the design of a driver's workstation on an agricultural machine, it is not constructive to use only the median of the height sitting (trunk length + head height) of a man (P₅₀=904 mm) as the term of reference: many men and also some women exist whose height sitting substantially exceeds the median (women P₉₅=905 mm; men P₉₅=958 mm). Persons such as these with individual values for the height sitting (trunk length + head height) exceeding the median could hit their heads against the roof of the machine were it to be designed against the median.

Likewise, design against the median length of the lower leg including foot (P₅₀=452 mm) is not expedient for specifying the seat surface height, for example in a tram. The values for the 5th percentile of men (P₅=410 mm) and the 5th percentile of women (P₅=380 mm) are more than 40 mm below this figure (if no allowance is made for footwear). Sitting on a seat surface that is too high results in the legs dangling and the edge of the seat surface exerting pressure upon the underside of the thigh. This may cause circulation to be obstructed, resulting in discomfort and pain.

The table below shows clearly by reference to the example of the body height and the body breadth sitting that the smaller dimensions are not always exclusive to women nor the larger dimensions to men. Owing to sex-specific patterns of proportion and fat distribution, the breadth and circumferential dimensions of the lower trunk half for women exceed the corresponding values for men in some cases (see Influence of the sex).